Summary Helicotylenchus microlobus is considered to be a junior synonym of H. pseudorobustus by several authors while others consider it as valid. To clarify the status of both species, 39 samples collected from various countries were subjected to statistical analyses that showed they could be grouped into six groups. Topotypes of H. pseudorobustus and H. microlobus belong to two different groups. However, samples in the other groups were morphologically intermediate between these two groups. Characters used in the past to uphold the validity of H. microlobus were variable and overlapping from group to group. The 28 samples studied are identified as H. pseudorobustus. Helicotylenchus microlobus, H. bradys and H. phalerus are confirmed as junior synonyms of H. pseudorobustus. There was no complete congruence between the morphological groups and molecular groups proposed by other authors. For these, two MOTU (Molecular Operational Taxonomic Unit) are accepted within H. pseudorobustus.

Aphelenchoides besseyi Christie, 1942 is recorded for the first time on rice in Mali and Upper Volta, the morphology is discussed and the description of the species emended. Boehmeria nivea Gaud. (Ramie) is reported as a new host for A. besseyi. A. siddiqii n.sp. is described from Foeniculum vulgare Mill, in Sudan. A key is given to the species of Aphelenchoides with a star tipped tail.

It is proposed to call "Index" the ratios traditionally included in nematode descriptions (ratios a, b, c, V, etc.) when they are used as a numerical expression of an ordered qualitative character (such as the shape or the position of an organ), and to reserve the name of "Ratios" to the entities recently reviewed by Roggen, Revets and Van den Berghe (Nemutofo&z, 1987). It is shown that it is always possible to use an index instead of an ordered qualitative character for describing a shape or a position, as long as the index is biologically related to the characteristic being described. Indexes are more objective than the corresponding qualitative characters. Also, they can be used in parametric statistical analyses, and in particular in discriminant function analyses.

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